I've been knitting for a short while and have just attempted to adapt a pattern for the first time. I have knitted a cardigan from the same pattern a couple of times so decided to adapt the pattern to make a pullover. I've completed all but the neck band and am now stuck! It's a 2 x 2 rib with a garter stitch border. My questions -

1 - is it possible to do the neck band on a straight needle or do I need a circular?

Welcome to KH!
You can certainly do the neckband on a straight needle. Instead of joining front and back at both shoulder, join only one shoulder and use the straight needles for the neckband.
I like a centered double decrease for the center decrease on a V-neck. It's shown on this video.http://www.youtube.com/watch?v=vjWrsQivZz0